Bacterial Endotoxins

About Endotoxins

Endotoxins, which occur in the outer membrane of certain gram-negative bacteria, are not secreted but are released only when the cells are disrupted or destroyed. Endotoxins are complex polysaccharide molecules that elicit an antigenic response, resulting in fever and altered resistance to bacterial infections. Exposure may cause toxic hemorrhagic shock and severe diarrhea.

Endotoxins are a combination of lipid (lipid A) and polysaccharide side chains and are integral components of the outer membrane of gram negative bacteria. Endotoxins are released into the surrounding environment during active cell growth or breakdown (lysis), or when bacterial cells are engulfed by immune cells called phagocytes.

In the 1930s and early 1940s, widespread outbreaks were reported of an acute, self-limited respiratory illness that appears to have been clinically identical to mill fever, but that also included chest tightness and cough much like symptoms of byssinosis. But rather than textile mill workers, those affected were poor rural families making mattresses for personal use from surplus, low-grade, stained cotton provided by a federally sponsored program.

“With our current knowledge, staining would be indicative of microbial growth on that cotton,” says Castellan. “And on subsequent investigation, it was found that this cotton was highly contaminated, much more than it normally is, with an enterobacter species, a gram negative bacteria.” The U.S. Public Health Service investigation of this outbreak resulted in the first scientific evidence suggesting that gram negative bacteria or its products are a likely cause of mill fever and possibly also a contributing factor in the etiology of acute and chronic pulmonary effects associated with byssinosis.

Endotoxins have been known to cause profound inflammation of any tissue exposed to them, including lung tissue. “Exposure to endotoxins causes an influx of inflammatory cells into the lungs,” says NIOSH immunologist Stephen A. Olenchock. “They bring with them and they release various agents called cytokines, which cause swelling, exudate, or seepage, from blood vessels. These are very potent inflammatory agents.”

Initially, the response to endotoxin may seem to be allergic. But unlike allergy, the active component is lipid A, and not an antigenic protein. “This is not an allergy at all,” Olenchock explains. “Allergy involves a type of antibody associated with a specific antigen. Here, there is an absence of antibody. Endotoxins activate the complement system, which causes inflammation and then removal of foreign agents.”

Occupational inhalation of endotoxins induces fever and constriction of airways. According to Castranova, endotoxins tend to upregulate the activity of lung phagocytes, encouraging pulmonary inflammation. “Many studies seem to show that if you put lung phagocytes in a test tube and add endotoxin, not much happens,” he explains. “But if you add endotoxin and then add a second stimulus, the [phagocytic] response to that second stimulus is greater than if the endotoxin weren’t there. The second stimulus could be the dust, the particulate matter.”

During April 30-July 26, 1998, 20 patients at a major medical center (hospital A) in Los Angeles County, California, developed severe shaking chills often accompanied by fever, tachycardia, and/or a decrease of greater than or equal to 20 mm Hg in systolic blood pressure within 3 hours after receiving intravenous (IV) gentamicin. Receipt of IV gentamicin was the only medication or procedure temporally associated with reactions among all of the patients. No deaths or serious sequelae were associated with the reactions. Similar incidents were reported by hospital personnel from six other states to CDC or the Food and Drug Administration (FDA) during April-August 1998. All reported reactions were associated with once-daily dosing regimens of gentamicin (lot numbers 170704, 180031, 180133, and 180191) produced by Fujisawa USA, Inc. (Deerfield, Illinois). * On August 13, the Los Angeles County Department of Health Services and CDC initiated an investigation with the assistance of hospital A personnel. This report summarizes the results of this investigation at hospital A, which found that gentamicin with endotoxin levels within the U.S. Pharmacopeia (USP) standards may deliver endotoxin amounts above the threshold for pyrogenic reactions with once-daily dosing.

A gentamicin-associated adverse reaction was defined as documented chills, rigors, or shivering within 3 hours after the start of IV gentamicin administration. A case-patient was defined as any hospital A patient aged greater than or equal to 28 days who had one or more gentamicin-associated adverse reactions from December 1, 1997, through August 25, 1998. Two schedules for gentamicin dosing were used: traditionally dosed (TD) gentamicin was defined as gentamicin administered at intervals of 8, 12, or 16 hours, and once-daily-dosed (ODD) gentamicin was defined as gentamicin administered at intervals of greater than or equal to 24 hours. The protocol for gentamicin dosing at hospital A is based on a dose of 7 mg/kg of body weight per day. Computerized pharmacy records were used to identify all patients who received gentamicin during three time periods: 1) the pre-epidemic period (December 1, 1997-January 15, 1998), before the suspected lots of Fujisawa gentamicin were delivered to the hospital; 2) the epidemic period (May 1-July 29, 1998), when the suspected lots of Fujisawa gentamicin were used; and 3) the postepidemic period (July 30-August 25, 1998), when gentamicin from another manufacturer was used. For the pre-epidemic period, the records of all patients who received ODD gentamicin from Fujisawa were reviewed. For the epidemic period, the records of all patients who received either ODD or TD gentamicin from Fujisawa during the first half of the 12-week epidemic period (May 1-June 15, 1998) were reviewed. For the postepidemic period, the records of all patients who received ODD gentamicin from another manufacturer were reviewed. Hospital A began using gentamicin from another manufacturer on July 29 with no other change in gentamicin administration policy or practices. Patients were excluded if they were aged less than 28 days, had incomplete medical records, or received both TD and ODD gentamicin during their hospital stay.

Of the 289 patients whose medical records were reviewed, 67 were excluded; eight because the patient was aged less than 28 days, 23 because medical record information was incomplete, and 36 because they received both TD and ODD gentamicin. Of the remaining 222 patients, 48 received gentamicin during the pre-epidemic period; 154, during the epidemic period (76 received TD gentamicin and 78 received ODD gentamicin); and 20, during the postepidemic period.

Of the 222 patients who received gentamicin, 24 had a gentamicin-associated reaction. Of these, two (8%) received gentamicin during the pre-epidemic period; 22 (92%), during the epidemic period; and none, during the postepidemic period. The mean age of case-patients was 40 years (range: 18-69 years), and 17 (71%) were women. Indications for gentamicin use included obstetric or gynecologic infections (12), fever and neutropenia (eight), gastrointestinal infections (three), or osteomyelitis (one). During the epidemic period, the adverse reaction rate among patients with ODD gentamicin (20 of 78) was significantly higher than that among patients with TD gentamicin (two of 76; relative risk {RR}=9.7; 95% confidence interval {CI}=2.4-40.3). In addition, among persons receiving ODD gentamicin, the adverse reaction rate during the epidemic period was significantly greater than during the pre-epidemic (two of 48; RR=6.15; 95% CI=1.5-25.2) or the postepidemic (none of 20; RR=indefinite; pless than 0.01) period. Among patients who received ODD gentamicin during the epidemic period, the weight of case-patients did not differ significantly from that of noncase-patients (mean weight: 162 lbs {73 kg}). Compared with noncase-patients, case-patients received higher doses (370 mg compared with 427 mg; p=0.01) and higher doses per kilogram of body weight (mean dose/kg body weight: 5.6 mg/kg compared with 6.2 mg/kg; pless than 0.01).

Samples of Fujisawa gentamicin from hospital A were examined for bacterial and/or endotoxin contamination. Bacterial cultures were negative. Endotoxin levels ranged from 25.6 to 32.0 endotoxin units (EU)/mL (median: 32 EU/mL); samples of gentamicin from another manufacturer that was used at hospital A had endotoxin levels less than 2.0 EU/mL. The USP limit for endotoxins in antibiotic formulations is 68 EU/mL or 1.7 EU/mg.